PZT MEMS resonant Lorentz force magnetometer

ABSTRACT

A MEMS magnetometer comprises a deflectable resonator comprising a base layer; a Lorentz force (LF) drive conductor attached to the base layer; and a piezoelectric sensor attached to the base layer and electrically isolated from the LF drive conductor. The LF drive conductor comprises conductive material configured for receiving a current at a mechanical resonant frequency of the device capable of causing mechanical deformation of the deflectable resonator, wherein the current causes formation of Lorentz forces in a presence of a magnetic field, and wherein the deflectable resonator is mechanically deformed as a result of the formation of the Lorentz forces. The mechanical deformation of the deflectable resonator generates a detectable piezoelectric electrical signal that is proportional to the magnitude of the magnetic field.

GOVERNMENT INTEREST

The embodiments of the invention described herein may be manufactured,used, and/or licensed by or for the United States Government.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The embodiments of the invention generally relate tomicroelectromechanical systems (MEMS) devices and microelectronicdevices, and, more particularly, to Lorentz force magnetometer devices.

2. Description of the Related Art

Conventional MEMS Lorentz force magnetometer designs, such as thosedescribed in U.S. Pat. No. 5,959,452, issued to Givens et al. on Sep.28, 1999, the complete disclosure of which is herein incorporated byreference, describe both optical and capacitive transduction schemes.This capacitive design has achieved a sensor resolution of approximately1 μT using a drive current of 1 mA and a Q-factor of 20,000, such assuggested by Wickenden et. al, “An Extremely Sensitive MEMS Magnetometerfor use as an Orientation Sensor on Projectiles,” Royal AeronauticalSociety Conference, Nanotechnology and Microengineering for FutureGuided Weapons, Nov. 11, 1999, the complete disclosure of which isherein incorporated by reference.

However, producing miniaturized optical MEMS devices, such asmagnetometers, generally appears to present substantial technicalchallenges including overcoming size, weight, and power consumptionparameters as well as attaining acceptable sensor resolution standards.In addition, the proposed piezoelectric devices appear to suffer frominappropriate design choices. Using the same electrode for driving theLorentz force current and piezoelectrically sensing those Lorentz forcesdirectly couples the drive and sense functions of the sensor; whichgenerally prevents the measurement of external magnetic fields. This mayalso severely limit the maximum drive currents of the device due to thelimited cross-sectional area and thermal/electrical material propertiesof the chosen conductor, platinum. Generally, the limited drive currentdirectly limits the sensitivity and resolution of such a device.

Accordingly, there remains a need for a novel MEMS magnetometer devicecapable of mapping magnetic fields in various applications, and which isfurther capable of achieving size, weight, power consumption, andresolution parameters previously unattainable by the conventionaldesigns.

SUMMARY OF THE INVENTION

In view of the foregoing, an embodiment of the invention provides amicroelectromechanical system (MEMS) magnetometer comprising adeflectable resonator comprising a base layer; a Lorentz force (LF)drive conductor attached to the base layer; and a piezoelectric sensorattached to the base layer and electrically isolated from the LF driveconductor. In one embodiment, the deflectable resonator comprises atorsional loop configuration. The LF drive conductor comprisesconductive material configured for receiving a current at a resonantfrequency capable of causing mechanical deformation of the deflectableresonator, wherein the current causes formation of Lorentz forces in thepresence of a magnetic field, and wherein the deflectable resonator ismechanically deformed as a result of the formation of the Lorentzforces. The piezoelectric sensor comprises a bottom electrode; apiezoelectric layer over and adjacent to the bottom electrode; a topelectrode over and adjacent to the piezoelectric layer; and an isolatorelectrically isolating the bottom electrode from the top electrode. TheMEMS magnetometer further comprises a first interconnect structureconnected to the LF drive conductor; and a second interconnect structureconnected to the piezoelectric sensor, wherein the second interconnectstructure is electrically isolated from the first interconnectstructure.

Another aspect of the invention provides a magnetometer comprising abase layer; a LF drive conductor attached to the base layer; and apiezoelectric sensor attached to the base layer and electricallyisolated from the LF drive conductor, wherein the LF drive conductorcomprises conductive material configured for receiving a current at aresonant frequency capable of causing mechanical deformation of the baselayer, the LF drive conductor, and the piezoelectric sensor, wherein thecurrent causes formation of Lorentz forces in the presence of a magneticfield, and wherein the base layer, the LF drive conductor, and thepiezoelectric sensor are mechanically deformed as a result of theformation of the Lorentz forces. The piezoelectric sensor comprises abottom electrode; a piezoelectric layer over and adjacent to the bottomelectrode; a top electrode over and adjacent to the piezoelectric layer;and an isolator electrically isolating the bottom electrode from the topelectrode. The magnetometer further comprises a first interconnectstructure connected to the LF drive conductor; and a second interconnectstructure connected to the piezoelectric sensor, wherein the secondinterconnect structure is electrically isolated from the firstinterconnect structure.

Another embodiment of the invention provides a method for detecting amagnetic field using a magnetometer comprising a deflectable resonatorcomprising a base layer; a LF drive conductor attached to the baselayer; and a piezoelectric sensor attached to the base layer andelectrically isolated from the LF drive conductor, wherein the methodcomprises placing the magnetometer in a magnetic field; applying acurrent to the LF drive conductor; and detecting a mechanicaldeformation of the deflectable resonator with a piezoelectricallygenerated electrical signal, wherein the amount of deformation of thedeflectable resonator is proportional to the piezoelectric signalgenerated by the piezoelectric sensor, which is then proportional to themagnitude of the magnetic field. The deflectable resonator comprises atorsional loop configuration according to one embodiment of theinvention.

Additionally, the LF drive conductor comprises conductive materialconfigured for receiving the current at a resonant frequency capable ofcausing the mechanical deformation of the deflectable resonator.Moreover, application of the current causes formation of Lorentz forces.Furthermore, the deflectable resonator is mechanically deformed as aresult of the formation of the Lorentz forces. The piezoelectric sensor,coupled mechanically to the LF drive conductor via the base layer, thendetects this deformation. The piezoelectric sensor comprises a bottomelectrode; a piezoelectric layer over and adjacent to the bottomelectrode; a top electrode over and adjacent to the piezoelectric layer;and an isolator electrically isolating the bottom electrode from the topelectrode. Also, the magnetometer further comprises a first interconnectstructure connected to the LF drive conductor; and a second interconnectstructure connected to the piezoelectric sensor, wherein the secondinterconnect structure is electrically isolated from the firstinterconnect structure.

Another aspect of the invention provides a method of forming amagnetometer, wherein the method comprises attaching a LF driveconductor to a base layer; attaching a piezoelectric sensor to the baselayer; and electrically isolating the piezoelectric sensor from the LFdrive conductor, wherein the LF drive conductor comprises conductivematerial. The piezoelectric sensor is formed by positioning apiezoelectric layer over and adjacent to a bottom electrode; positioninga top electrode over and adjacent to the piezoelectric layer; andpositioning an electrical isolator between the bottom electrode and thetop electrode. The method further comprises connecting a firstinterconnect structure to the LF drive conductor; and connecting asecond interconnect structure to the piezoelectric sensor, wherein thesecond interconnect structure is electrically isolated from the firstinterconnect structure.

The embodiments of the invention provide a lead zirconate titanate (PZT)MEMS resonant Lorentz force magnetometer that avoids conventional designflaws and functions properly as a quasi-static or dynamic magnetic fieldsensor that is small in size, weight, power consumption, providesexcellent sensor resolution, possesses a large dynamic range, and has alow cost of manufacturing.

These and other aspects of the embodiments of the invention will bebetter appreciated and understood when considered in conjunction withthe following description and the accompanying drawings. It should beunderstood, however, that the following descriptions, while indicatingpreferred embodiments of the invention and numerous specific detailsthereof, are given by way of illustration and not of limitation. Manychanges and modifications may be made within the scope of theembodiments of the invention without departing from the spirit thereof,and the embodiments of the invention include all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention will be better understood from thefollowing detailed description with reference to the drawings, in which:

FIG. 1 is a perspective view of an initial wafer stack used forprocessing a magnetometer device according to an embodiment of theinvention;

FIG. 2 is a side view of the partially completed magnetometer device ofFIG. 1 according to an embodiment of the invention;

FIG. 3 is a perspective view of a partially completed magnetometerdevice illustrating a first processing step according to an embodimentof the invention;

FIG. 4 is a perspective view of a partially completed magnetometerdevice illustrating a second processing step according to an embodimentof the invention;

FIG. 5 is a perspective view of a partially completed magnetometerdevice illustrating a third processing step according to an embodimentof the invention;

FIG. 6 is a perspective view of a partially completed magnetometerdevice illustrating a fourth processing step according to an embodimentof the invention;

FIG. 7 is a perspective view of a partially completed magnetometerdevice illustrating a fifth processing step according to an embodimentof the invention;

FIG. 8 is a magnified perspective view of the encircled dotted area “AA”of the magnetometer device of FIG. 7 according to an embodiment of theinvention;

FIG. 9 is a perspective view of a partially completed magnetometerdevice illustrating a sixth processing step according to an embodimentof the invention;

FIG. 10 is a perspective view of a partially completed magnetometerdevice illustrating a seventh processing step according to an embodimentof the invention;

FIG. 11 is a perspective view of a completed magnetometer deviceillustrating a final processing step according to an embodiment of theinvention;

FIG. 12 is a magnified perspective view of the encircled dotted area“BB” of the magnetometer device of FIG. 11 according to an embodiment ofthe invention;

FIG. 13 is a magnified perspective view of the encircled dotted area“CC” of the magnetometer device of FIG. 11 according to an embodiment ofthe invention;

FIG. 14 is an isolated perspective view of the Lorentz force driveconductor component of the magnetometer device of FIG. 11 according toan embodiment of the invention;

FIG. 15 is an isolated perspective view of the piezo sensor component ofthe magnetometer device of FIG. 11 according to an embodiment of theinvention;

FIG. 16 is an isolated perspective view of the interconnect component ofthe magnetometer device of FIG. 11 according to an embodiment of theinvention;

FIG. 17 is a cross-sectional view of the encircled dotted area “DD” ofthe magnetometer device of FIG. 13 according to an embodiment of theinvention;

FIG. 18 is a perspective view of the magnetometer device of FIG. 11 inthe presence of an external magnetic field, B, according to anembodiment of the invention;

FIG. 19 is a perspective view of the magnetometer device of FIG. 11during the application of an AC current, I, being applied to the Lorentzforce conductor component of FIG. 14 according to an embodiment of theinvention;

FIG. 20 is a perspective view of the magnetometer device of FIG. 11illustrating the resulting Lorentz forces, F_(Lorentz), during operationof the device in the manner illustrated in FIGS. 18 and 19 according toan embodiment of the invention; and

FIG. 21 is a flow diagram illustrating a preferred method according toan embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The embodiments of the invention and the various features andadvantageous details thereof are explained more fully with reference tothe non-limiting embodiments that are illustrated in the accompanyingdrawings and detailed in the following description. It should be notedthat the features illustrated in the drawings are not necessarily drawnto scale. Descriptions of well-known components and processingtechniques are omitted so as to not unnecessarily obscure theembodiments of the invention. The examples used herein are intendedmerely to facilitate an understanding of ways in which the embodimentsof the invention may be practiced and to further enable those of skillin the art to practice the embodiments of the invention. Accordingly,the examples should not be construed as limiting the scope of theembodiments of the invention.

As mentioned, there remains a need for a novel MEMS magnetometer devicecapable of mapping magnetic fields in various applications, and which isfurther capable of achieving size, weight, power consumption, andresolution parameters previously unattainable by the conventionaldesigns. The embodiments of the invention achieve this by providing aPZT MEMS resonant Lorentz force magnetometer that avoids conventionaldesign flaws and functions properly as a quasi-static or dynamicmagnetic field sensor that is small in size, weight, power consumption,provides excellent sensor resolution, possesses a large dynamic range,and has a low cost of manufacturing. Referring now to the drawings andmore particularly to FIGS. 1 through 21 where similar referencecharacters denote corresponding features consistently throughout thefigures, there are shown preferred embodiments of the invention.

The process for fabricating the PZT MEMS resonant Lorentz forcemagnetometer 1 is generally depicted in FIGS. 1 through 11, with thecompleted magnetometer device 1 shown in FIG. 11. Moreover, multipleoptions exist for process specifics of most of the processing steps, andthe embodiments of the invention are not limited to one particularprocessing technique. As shown in FIGS. 1 and 2, the starting processingmaterial is a silicon (Si) substrate wafer 8 having an approximatethickness of 450 μm. Next, a plasma enhanced chemical vapor deposition(PECVD) of silicon dioxide (SiO₂) is performed over the silicon wafer 8,thereby forming a SiO₂ base layer 10. The thickness of the silicondioxide base layer 10 may vary between 0.5 μm and 2 μm in thickness,depending on the choice for the overall dimensions of the resonator, thethickness of the LF conductor, and the thickness of the PZT. Then, atitanium/platinum (Ti/Pt) bottom electrode 12 is sputter deposited overthe SiO₂ base layer 10. The titanium layer is approximately 0.02 μm andthe platinum layer is approximately 0.08 μm in thickness. Next, sol-gellead zirconate titanate (PZT) 14 is spin coated over the Ti/Pt bottomelectrode 12. The thickness of the PZT 14 may vary from 0.5 μm to 1 μmin thickness, again depending on the choice for the overall dimensionsof the resonator, the thickness of the LF conductor, and the thicknessof the base layer. While PZT is a preferred material, otherpiezoelectric materials could also be used in accordance with theembodiments of the invention.

FIG. 3 illustrates a liftoff process occurring with sputtered Pt ofapproximately 0.1 μm used to define the top electrode 16. Thereafter, asillustrated in FIG. 4, an ion milling process of the PZT layer 14 andTi/Pt bottom electrode 12 occurs down to SiO₂ base layer 10. As shown inFIG. 4, portions of the PZT layer 14 remain as does the top electrode16. This ion milling process generally provides electrical isolation ofthe subsequent sensor components of the magnetometer device 1.

Next, as depicted in FIG. 5, a reactive ion etching (RIE) process of theSiO₂ base layer 10 occurs down to the silicon substrate wafer 8, whichhelps define the subsequent resonator component of the magnetometerdevice 1 and enable its ultimate release from the silicon substratewafer 8. In FIG. 6, a PECVD of a second SiO₂ layer 18 occurs over theexposed portions of the PZT layer 14, top electrode 16, Si substratewafer 8, and the first SiO₂ layer 10. Next, as shown in FIG. 7, a RIEprocess occurs to remove the second SiO₂ layer 18 except for a smallportion forming a pair of thin isolation posts (i.e., isolators) 17. Theisolation posts 17, which comprise the second SiO₂ layer 18, are shownin the encircled dotted portion “AA” in FIG. 7, which is furtherillustrated with greater magnification in FIG. 8.

As shown in FIG. 8, the isolation posts 17 surround a narrow anchoredportion of the PZT layer 14 as well as an upper and side surface of asmall portion of the top electrode 16 near the piezoelectric bond padportion 19 of the magnetometer 1. The isolation posts 17 form apassivated path for subsequent top electrode traces to be depositedthereon. Without the isolation posts 17, the top and bottom electrodes16, 12, respectively, would cause an undesirable short circuit in themagnetometer 1. Accordingly, this process allows the top electrode bondpads 23 (shown in FIG. 11) to be deposited onto the second SiO₂ layer 18as opposed to the PZT 14 itself, which significantly reduces theparasitic capacitance of the top electrode bond pads 23, therebyreducing sensor noise. Thereafter, the PZT 14 is removed from the bottomelectrode bond pad portion 19 via wet etching, as depicted in FIG. 9. Asshown in FIG. 10, a highly electrical and thermally conductive material20 such as titanium copper (TiCu) or titanium gold (TiAu) is depositedand patterned to form the Lorentz force (LF) drive conductor component 3(shown in isolation in FIG. 14) of the magnetometer 1. The thickness ofthe conductive material 20 depends on the exact dimensions of theresonator, the thickness of the PZT layer 14, and the thickness of theSiO₂ base layer 10; but is typically between 1 μm and 2.5 μm. The LFdrive conductor component 3 provides the path for the drive currentloops around the perimeter of the magnetometer device 1. The completedmagnetometer device 1 is shown in FIG. 11 upon formation (throughwell-known deposition and patterning techniques) of 0.5 μm of the TiAutop electrode bond pads 23 (formed over the bond pad portion 19), traces24, and LF conductor bond pads 22. Finally, a xenon difluoride (XeF₂)isotropic etching process occurs to remove exposed portions of thesilicon substrate wafer 8.

If the conductive material 20 is formed of TiCu, then the process occursas generally described above. However, if the conductive material 20 isformed of TiAu, then the last two processing steps involving theformation of the LF drive conductor component 3 and the top electrodebond pads 23 may be combined because the same material (TiAu) is usedfor each respective formation. Generally, TiCu has superior thermal andelectrical properties. Typically, TiCu generates approximately half ofthe heat that TiAu does. This enables a larger drive current to besupplied to the device, thereby resulting in greater sensor performance.

The various interconnect components such as the top electrode bond pads23, traces 24, and LF conductor bond pads 22 are further illustrated inFIGS. 12 and 16, which are a magnified perspective view of the bond padportion 19 (encircled dotted area “BB” shown in FIG. 11) of themagnetometer device 1 and an isolated perspective view of theinterconnect components, respectively. The MEMS resonator component 2 ofthe magnetometer device 1 is shown in the isolated view shown in FIG.13, which generally comprises the encircled dotted area “CC” of themagnetometer device 1 shown in FIG. 11. The MEMS resonator component 2is released from the silicon substrate wafer 8 (not shown in FIG. 13) bythe performance of the above-mentioned XeF₂ isotropic etching process.Thus, the MEMS resonator component 2 can be thought of as a freetorsional current loop. However, other geometric configurations couldalso be used. For example, a clamped cantilever array design could beused (not shown) as well as other configurations depending on theparticular application of the magnetometer 1.

The piezoelectric sensor component 4 of the magnetometer device 1 ofFIG. 11 is shown in the isolated view of FIG. 15. The piezoelectricsensor component 4, which comprises the TiPt bottom electrode 12, PZTlayer 14, and Pt top electrode 16, senses the deformation of the MEMSresonator component 2 due to Lorentz forces. In FIG. 16, the topelectrode bonds pads 23 are for the LF drive conductor component 3 (ofFIG. 14) and the LF conductor bonds pads 22 are for the piezoelectricsensor component 4 (of FIG. 15). A cross-sectional view of the encircleddotted area “DD” of the magnetometer device of FIG. 13 is shown in FIG.17, where an air gap 26 exists between the conductive material 20 of theLF drive conductor component 3 and the TiPt/PZT/Pt piezoelectric sensorcomponent 4 thereby creating electrical isolation between the LF driveconductor component 3 and the TiPt/PZT/Pt piezoelectric sensor component4. Each of the LF drive conductor component 3 and the TiPt/PZT/Ptpiezoelectric sensor component 4 is mechanically coupled to the firstSiO₂ layer 10. However, because the first SiO₂ layer 10 is insulative,there remains electrical isolation between the LF drive conductorcomponent 3 and the TiPt/PZT/Pt piezoelectric sensor component 4.Without the electrical isolation, the drive function of the sensor(generation of the Lorentz forces) would be directly coupled to thesense function of the sensor (piezoelectric detection of the Lorentzforces). Piezoelectric materials can act as sensors (generation ofelectrical charge due to mechanical stress) and conversely as actuators(generation of mechanical strain due to electrical field). Therefore,without electrical isolation the drive signal would otherwise cause theTiPt/PZT/Pt piezoelectric sensor component 4 to actuate, and not sense.

FIGS. 18 through 20 illustrate the magnetometer device 1 in operation.As shown in FIG. 18, the magnetometer device 1 is placed in the presenceof an external magnetic field, B (generally indicated by the series ofarrows in FIG. 18 traversing the magnetometer device 1). Then, as shownin FIG. 16 and FIG. 19, an AC voltage source (not shown) is appliedacross the pair of electrode bond pads 23 to generate an AC current, I,which flows through the LF drive conductor component 3, looping aroundthe perimeter therein. Next, as depicted in FIG. 20, the resultingLorentz forces, F_(Lorentz), are normal to both the current and magneticfield vectors. These Lorentz forces cause mechanical deformation in theMEMS resonator component 2. The AC drive current, I, is at a resonantfrequency of the MEMS resonator component 2, which amplifies thedeformation by the mechanical quality factor of the chosen resonantmode. The deformed piezoelectric produces an AC current that isproportional to the deformation. This, in turn, is proportional to theLorentz forces, F_(Lorentz), and hence the external magnetic field. Thefollowing analytical models demonstrate the validity of these concepts.

An experimental analytical model was developed to facilitate the choiceof design variables used in accordance with the embodiments of theinvention. The analytical model can accommodate simple geometries suchas cantilevers, free-free, and clamped-clamped beams. The modelapproximates many of the designs; the torsional current loop designs inparticular have resonant bending dominated modes that behave much likecantilevers. The following are the relevant variables employed in thefollowing equations:

TABLE 1 Relevant Variables n number of electrodes b electrode width hdistance from the neutral axis to the midplane of the piezo e₃₁piezoelectric stress constant Q resonator quality factor λ_(I) Ithresonant mode number ΔT_(max) maximum allowable temperature of LFconductor σ_(con) electrical conductivity of LF conductor ρ_(con) massdensity of LF conductor c_(con) specific heat of LF conductor A_(con)cross-sectional area of LF conductor L beam length φ constant depends onmechanical boundary conditions EI_(comp) flexural rigidity of compositestructure μ mass per unit length of composite structure N mechanicaltime constant multiplier

The goal is to derive an expression for the current sensitivity of thedevice with respect to a static magnetic field (Eq. 1) due to theLorentz force (Eq. 2). The piezoelectrically generated current generatedcan be expressed in terms of the angular deflection of the cantileversfree end due to the Lorentz force acting upon it (Eq. 3).

$\begin{matrix}{S_{mag} = {\frac{PiezoCurrent}{MagneticFieldIntensity} = \frac{{\overset{.}{q}}_{piezo}}{\overset{arrow}{B}}}} & ( {{Eq}.\mspace{14mu} 1} )\end{matrix}$

_(Lorentz max)=

_(max)l

  (Eq. 2){dot over (q)}_(piezo)=θ_(res)bnωhe₃₁  (Eq. 3)

For a cantilever geometry, the angular deflection of the free end of thebeam at resonance is expressed in terms of the distributed load actingupon it and the mechanical quality factor (Eq. 4). Substituting (Eq. 2)and (Eq. 4) into (Eq. 3), the piezoelectrically generated current due toa Lorentz force induced by a static magnetic field and an AC current ata mechanical resonance frequency of the cantilever beam is obtained (Eq.5). Substituting the resonance frequency (Eq. 6) into (Eq. 5), dividingout the magnitude of the magnetic field, and simplifying, the continuousdrive current sensitivity of the device (Eq. 7) is obtained.

$\begin{matrix}{\theta_{res} = \frac{F_{tot}L^{2}Q}{6({EI})_{comp}}} & ( {{Eq}.\mspace{14mu} 4} ) \\{{\overset{.}{q}}_{piezo} = \frac{{nbh}\;\omega\; e_{31}{QI}_{\max}{BL}^{3}}{6({EI})_{comp}}} & ( {{Eq}.\mspace{14mu} 5} ) \\{\omega_{res} = {\frac{\lambda}{2\pi}\sqrt{\frac{({EI})_{comp}}{\mu\; L^{4}}}}} & ( {{Eq}.\mspace{14mu} 6} ) \\{S_{{mag}_{{Im}\;{ax}}} = \frac{n\;\lambda_{i}{bhe}_{31}{LQI}_{\max}}{12\pi\sqrt{{EI}_{comp}\mu}}} & ( {{Eq}.\mspace{14mu} 7} )\end{matrix}$

Ignoring heat transfer factors, the maximum drive current can beexpressed in terms of the maximum temperature, the thermal materialproperties of the conductor, the cross-sectional area, and the durationof the application of the current (Eq. 8). The minimum pulse durationcan be represented by a safety factor divided by the resonant qualityfactor and the resonant frequency (Eq. 9). Substituting (Eq. 8) and (Eq.9) into (Eq. 7) and simplifying yields the expression for the pulseddrive current sensitivity of the device (Eq. 10).

$\begin{matrix}{I_{\max} = \sqrt{\frac{\Delta\; T_{\max}\sigma\;\rho\;{cA}_{con}^{2}}{t_{pulse}}}} & ( {{Eq}.\mspace{14mu} 8} ) \\{{t_{pulse} \approx {N\;\tau_{mech}}} = \frac{N}{Q\;\lambda_{i}\sqrt{\frac{{EI}_{comp}}{\mu\; L^{4}}}}} & ( {{Eq}.\mspace{14mu} 9} ) \\{S_{{mag}_{Pulse}} = \frac{{{nbhe}_{31}( {\lambda_{i}Q} )}^{\frac{3}{2}}\sqrt{\Delta\;{T_{\max}( {\sigma\;\rho\;{cA}^{2}} )}_{con}}}{\phi\;{\pi( {EI}_{comp} )}^{\frac{1}{4}}\mu^{\frac{3}{4}}\sqrt{N}}} & ( {{Eq}.\mspace{14mu} 10} )\end{matrix}$

The EI_(comp) term in the previous equations is the bending stiffness orflexural rigidity of the composite cantilever structure. The area momentof inertia (I_(comp)) of a cross-section of the beam with respect to they-axis of the composite beam is the summation of the sums of the momentsof inertia of each layer and the product of each layer's cross-sectionalarea and the square of the distance from the neutral axis to thecentroidal axis of each layer, as given by the parallel axis theorem.The composite modulus of elasticity (E_(comp)) is the summation of theproducts of volume fractions of each layer and the modulus of thecorresponding layer. For a constant width beam, the composite bendingstiffness is (Eq. 11). The h term in the previous equations is thedistance between the center of the piezoelectric layer and the overallstructure's neutral plane. The location of the neutral axis is found bydividing the summation of the products of the layer cross sectionalareas and the distances from the centroids of the layers to somearbitrary reference axis by the cross-sectional area of the entire beamand the expression for h is given by (Eq. 12). The term h_(piezo) ismeasured relative to the same arbitrary reference axis used to definethe location of the neutral axis.

$\begin{matrix}{{EI}_{comp} = \frac{{\Sigma( {t_{layer}E_{layer}} )}{\Sigma( {I_{layer} + {A_{layer}d_{layer}^{2}}} )}}{t_{beam}}} & ( {{Eq}.\mspace{14mu} 11} ) \\{h = {{( h_{piezo} ) - ( \frac{\Sigma( {A_{layer}y_{layer}} )}{A_{total}} )}}} & ( {{Eq}.\mspace{14mu} 12} )\end{matrix}$

The design provided by the embodiments of the invention mechanicallycouples the LF drive conductor component 3 (drive function) and thepiezoelectric sensor component 4 (sense function) by means of attachingboth components (LF drive conductor component 3 and piezoelectric sensorcomponent 4) to a separate structure (i.e., the silicon dioxide baselayer 10). Furthermore, the design provided by the embodiments of theinvention electrically decouples LF drive conductor component 3 (drivefunction) and the piezoelectric sensor component 4 (sense function) bymeans of physically separating the LF drive conductor from thepiezoelectric sensor component 4 using isolators 17.

In an alternative embodiment, a DC current may be applied to the LFdrive conductor component 3. However, if an AC current is used, asdescribed above, then the resonator quality factor, Q, amplifies thedevice sensitivity by as much as 10,000. The magnetic fields that can besensed at a high Q resonant mode is approximately “Q” times smaller thanat static conditions (i.e., DC drive). This means that the sensor is farsuperior at operating with a high Q as opposed to a low Q.

The embodiments of the invention provides a PZT MEMS resonant Lorentzforce magnetometer 1 that avoids conventional design flaws and functionsproperly as a quasi-static or dynamic magnetic field sensor. Moreover,the magnetometer 1 is small in size (much less than a squarecentimeter), weight (milli-microgram mass), power consumption (in themilliwatt range), provides excellent sensor resolution (approximately 1nanoTesla, possesses a large dynamic range (approximately 80 dB), andhas a low cost of manufacturing. The magnetometer device 1 can measure 1Tesla through 1 nanoTesla field strengths. The large dynamic range isattainable due to the ability to scale the LF drive current to preventoverdriving of the magnetometer device 1 in strong fields that wouldotherwise destroy the magnetometer device 1.

Another aspect of the invention is illustrated in the flowchart of FIG.21, which includes descriptions which refer to components provided inFIGS. 1 through 20. FIG. 21 illustrates a method for detecting amagnetic field, B, using a magnetometer 1 comprising a deflectableresonator 2 comprising a base layer 10; a LF drive conductor 3 attachedto the base layer 10; and a piezoelectric sensor 4 attached to the baselayer 10 and electrically isolated from the LF drive conductor 3,wherein the method comprises placing (101) the magnetometer 1 in amagnetic field, B; applying (103) a current, I, to the LF driveconductor 3; and detecting (105) a mechanical deformation of thedeflectable resonator 2, through the piezoelectrically generated signalof the piezoelectric sensor 4, wherein the amount of deformation of thedeflectable resonator 2 is proportional to the piezoelectric signalwhich is then proportional to the magnitude of the magnetic field, B.

The deflectable resonator 2 comprises a torsional loop configurationaccording to one embodiment of the invention. Additionally, the LF driveconductor 3 comprises conductive material 20 configured for receivingthe current, I, at a resonant frequency capable of causing themechanical deformation of the deflectable resonator 2. Moreover,application of the current, I, in the presence of a magnetic field, B,causes formation of Lorentz forces, F_(Lorentz), wherein the Lorentzforces, F_(Lorentz), are in a plane normal to the current vector, I, andthe magnetic field vector, B. Furthermore, the deflectable resonator 2is mechanically deformed as a result of the formation of the Lorentzforces, F_(Lorentz).

Moreover, the piezoelectric sensor 4 comprises a bottom electrode 12; apiezoelectric layer 14 over and adjacent to the bottom electrode 12; atop electrode 16 over and adjacent to the piezoelectric layer 14; and anisolator 17 electrically isolating the bottom electrode 12 from the topelectrode 16. Also, the magnetometer 1 further comprises a firstinterconnect structure 23 connected to the LF drive conductor 3; and asecond interconnect structure 22 connected to the piezoelectric sensor4, wherein the second interconnect structure 22 is electrically isolatedfrom the first interconnect structure 23.

The magnetometer 1 is capable of being utilized in several applicationsincluding quasi-static and dynamic magnetic field sensing for detectionof ferrous objects by means of sensing the disturbances in the Earth'slocal magnetic field generated by the ferrous objects. Furthermore, themagnetometer 1 may be used for orientation sensing of projectiles usedin military and non-military environments.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationssuch specific embodiments without departing from the generic concept,and, therefore, such adaptations and modifications should and areintended to be comprehended within the meaning and range of equivalentsof the disclosed embodiments. It is to be understood that thephraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the embodiments ofthe invention have been described in terms of preferred embodiments,those skilled in the art will recognize that the embodiments of theinvention can be practiced with modification within the spirit and scopeof the appended claims.

1. A configurable microelectromechanical system (MEMS) magnetometercomprising a deflectable resonator comprising: a base layer; a Lorentzforce (LF) drive conductor attached to said base layer; and apiezoelectric sensor attached to said base layer and electricallyisolated from said LF drive conductor wherein said MEMS system iscapable of processing maximum drive current equivalent to the maximumcurrent of the Lorentz force drive conductor.
 2. The MEMS magnetometerof claim 1, wherein said deflectable resonator comprises a torsionalloop configuration.
 3. The MEMS magnetometer of claim 1, wherein said LFdrive conductor comprises conductive material configured for receiving acurrent at a resonant frequency capable of causing mechanicaldeformation of said deflectable resonator at one or more of a pluralityof resonant frequencies.
 4. The MEMS magnetometer of claim 3, whereinsaid current causes formation of Lorentz forces in a presence of amagnetic field.
 5. The MEMS magnetometer of claim 4, wherein saiddeflectable resonator is mechanically deformed as a result of theformation of said Lorentz forces.
 6. The MEMS magnetometer of claim 1,wherein said piezoelectric sensor comprises: a bottom electrode; apiezoelectric layer over and adjacent to said bottom electrode; a topelectrode over and adjacent to said piezoelectric layer; and an isolatorelectrically isolating said bottom electrode from said top electrode. 7.The MEMS magnetometer of claim 1, further comprising: a firstinterconnect structure connected to said LF drive conductor; and asecond interconnect structure connected to said piezoelectric sensor,wherein said second interconnect structure is electrically isolated fromsaid first interconnect structure.
 8. The MEMS magnetometer of claim 1,wherein said electrical isolation further comprises a silicon dioxideisolator.
 9. A method for detecting a magnetic field using amagnetometer comprising a deflectable resonator comprising a base layer;a Lorentz force (LF) drive conductor attached to said base layer; and apiezoelectric sensor attached to said base layer and electricallyisolated from said LF drive conductor, said method comprising: placingsaid magnetometer in a magnetic field; applying an AC currentcorresponding to a mechanical resonant frequency of the resonator tosaid LF drive conductor; and detecting a mechanical deformation of saiddeflectable resonator with a piezoelectrically generated signal, whereinan amount of deformation of said deflectable resonator is proportionalto a piezoelectric signal generated by said piezoelectric sensor, andwherein said piezoelectric signal is proportional to a magnitude of saidmagnetic field.
 10. The method of claim 9, wherein said deflectableresonator comprises a torsional loop configuration.
 11. The method ofclaim 9, wherein said LF drive conductor comprises conductive materialconfigured for receiving said current at a resonant frequency capable ofcausing said mechanical deformation of said deflectable resonator. 12.The method of claim 11, wherein application of said current causesformation of Lorentz forces.
 13. The method of claim 12, wherein saiddeflectable resonator is mechanically deformed as a result of theformation of said Lorentz forces, and wherein said piezoelectric sensordetects said mechanical deformation.
 14. The method of claim 9, whereinsaid piezoelectric sensor comprises: a bottom electrode; a piezoelectriclayer over and adjacent to said bottom electrode; a top electrode overand adjacent to said piezoelectric layer; and an isolator electricallyisolating said bottom electrode from said top electrode.
 15. The methodof claim 9, wherein said magnetometer further comprises: a firstinterconnect structure connected to said LF drive conductor; and asecond interconnect structure connected to said piezoelectric sensor,wherein said second interconnect structure is electrically isolated fromsaid first interconnect structure.
 16. The method of claim 9, furthercomprising forming said isolator from silicon dioxide.